How do we know God's will? There are two sides of God's will. God's revealed will is written in the Bible. The word of God is the will of God. We can know God's will for us by reading the Bible. The secret will of God is not revealed (Deuteronomy 29:29). Believers are responsible to do the revealed will of God.
Paul's prayer in Romans 1:8-15 is an example of both the revealed and secret will of God. He prayed that God would make a way for him to visit the church at Rome. Also, God's permissive will allowed him to be hindered by circumstances to visit there. He realized the providence of God rules over all our circumstances (Romans 8:28). When God would permit him to visit there, he did not know.
The apostle Paul knew the revealed will of God for the church at Rome. They were to know the spiritual gifts God had for them. Every believer has a ministry gift. Paul mentioned seven such gifts in Romans 12:6-8. It was God's will to encourage them and strengthen the church. It is God's will for all people everywhere to hear the gospel of Jesus Christ. Every believer should share the gospel. The primary purpose of the apostle Paul and the church is to spread the gospel of Christ.
Know God's will through the word of God. Then, you will "be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God" (Romans 12:2). Remember, God's will is good. The word of God is the will of God.